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More Moon and Venus

StarDate:

August 10, 2013

When early robotic landers took a peek at the lunar sunset, they saw something odd. Since the Moon is basically airless, there should be no twilight on the Moon — the sky should go dark as soon as the Sun dips below the horizon. But the Surveyor landers saw a thin band of light that persisted well after the Sun had disappeared. Scientists have speculated that the glow was caused by sunlight reflecting off of tiny grains of electrically charged dust that were “levitating” above the surface.

Scientists hope to learn whether that’s the case with the help of the latest lunar explorer — a robotic orbiter known as LADEE. It’s scheduled for launch as early as next month.

The probe will study the thin lunar atmosphere. Although it’s basically a hard vacuum, there are a few atoms of hydrogen, helium, and other elements. Some of these elements may be particles of the solar wind that were captured by the Moon. Others may be bits of moonrocks chipped off the surface by the solar wind or by the impacts of space rocks. LADEE will measure the lunar atmosphere’s composition, which will reveal more about its origins.

LADEE also will look for the same type of glow seen by Surveyor and by Apollo astronauts in lunar orbit. That’ll tell us whether dust grains really do float above the surface of the Moon.

The Moon is in beautiful view tonight. It’s a thin crescent quite low in the sky shortly after sunset, with Venus, the “evening star,” directly to its right.

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